Granular bitumen coated with carbon black or silica

ABSTRACT

A free-flowing granular bitumen product containing from 0.5 to 6% by weight of a powdery coating and separating agent such as synthetic silica or carbon black is prepared by atomizing hot, liquid bitumen in a spray mixer while simultaneously introducing the powdery coating and separating agent by means of the cold air flow into the spray mixer.

The present invention relates to a granular bitumen product and theprocess for its manufacture.

INTRODUCTION AND BACKGROUND

Bitumen is a petroleum product obtained by a process of refining thepetroleum. Bitumen is a high molecular weight mixture of hydrocarbons,with a dark color; ranging in viscosity from a barely fluid, sticky to abrittle consistency. It is further characterized by hydrophobicproperties (see DIN 55 946).

Because of its thermoplastic behavior, bitumen is easily worked at hightemperatures.

For most applications, for instance in making asphalt mixes for roadconstruction or bituminous roofings, the bitumen must be delivered inthe heated, fluid state from the refinery and must be kept ready ininsulated storage tanks.

It is known to make a powdery bitumen concentrate with a content insilica of 10 to 80% by weight by spraying the liquid bitumen onto thesilica (German Patent 29 33 339).

The known bitumen concentrates are used in the industry to enhance thetoughness properties of asphalt mixes employed for road construction.

The known bitumen concentrate suffers from the drawback that because ofits high silica content, dilution by means of further bitumen (binder)always is required during processing.

Accordingly, there is a need for a friable, i.e. free-flowing, bitumenwhich can be added directly; that is without being molten first, to themineral mix, without addition of further liquid or solid binder.Further, there is a need to avoid the often undesired stiffening due tothe high proportion of silica.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a friable, granularbitumen product containing between 0.5 and 6% by weight of powderycoating substance and separating agent such as synthetic silica orcarbon black.

In a more detailed and preferred aspect of the invention, the content inpowdery coating material and separating agent is between 1.5 and 3% byweight.

The bulk density of the free-flowing granular bitumen product o theinvention is between 400 and 800 g/liter (measured per DIN 53,912).

The particle size of the granular bitumen product of the invention isbetween 500 and 700 microns (μ).

All known kinds of bitumens may be used as the starting bitumensubstance of the present invention. Especially suitable bitumen typesfor purposes of the present invention are those that are solid at roomtemperature.

Softer types of road construction bitumens, such as B 200, are hardlysuitable.

The powdery cladding or coating material and separation agents that areuseful in connection with the granular bitumen according to theinvention are synthetic silicas prepared pyrogenically or byprecipitation, or carbon black. All such substances and their respectivemethods of preparation are known in the art.

Suitable synthetic silicas for preparing the granular bitumen productsof the present invention are, for instance, those described inWINNACKER-KUECHLER, Chemische Technologie, Vol. 3, AnorganischeTechnologie II, 4th edition, Carl Hauser Verlag, Munich, Vienna, 1983,pp. 75-90, incorporated herein by reference.

Pyrogenic silica prepared by flame hydrolysis, and further,precipitation silicas are especially useful, preference being given tosilicas made by the well known precipitation technology.

The precipitated silicas may be used unground or ground, spray-dried orspray-dried and ground.

Illustratively, the following precipitated silicas may be used, thepreferred precipitated silica is identified by the trade name SIPERNAT22 LS:

    __________________________________________________________________________                FD 320    Sipernat                                                                           Sipernat                                                                           Sipernat                                                  DS   Durosil                                                                            22   22 S 22 LS                                         __________________________________________________________________________    BET surface                                                                            m.sup.2 g                                                                        170  60   190  190  190                                           area.sup.1                                                                    Average primary                                                                        nm 18   40   18   18   4.5                                           particle                                                                      size                                                                          Tamped   g/l                                                                              80   210  270  120  80                                            density.sup.2                                                                 pH value.sup.3                                                                            6.3  9    6.3  6.3  6.3                                           Sifting  %  0.01 0.3  0.5  0.1  0.1                                           Residue                                                                       (acc. Mocker)                                                                 (45 μm).sup.4                                                              Drying loss (2h,                                                                       %  6    6    6    6    6                                             105° C.).sup.5                                                         Ignition loss (2h,                                                                     %  5    6    5    5    5                                             1000° C.).sup.5 6                                                      SiO.sub.2.sup.7                                                                        %  98   98   98   98   98                                            Na.sub.2 O.sup.7                                                                       %  1    1    1    1    1                                             Fe.sub.2 O.sub.3.sup.7                                                                 %  0.03 0.03 0.03 0.03 0.03                                          SO.sub.3.sup.7                                                                         %  0.8  0.8  0.8  0.8  0.8                                           __________________________________________________________________________     .sup.1 DIN 66 131                                                             .sup.2 DIN 53 194 (unsifted), ISO 787/XI or JIS K 5101/18                     .sup.3 DIN 53 200 (in 5% aqueous dispersion) ISO 787/IX, ASTM D 1208 or       JIS K 5101/24                                                                 .sup.4 DIN 53 580, ISO 787/XVII or JIS K 5101/20                               .sup.5 DIN 55 921, ASTM D 1208 or JIS K 5101/23                              .sup.6 referred to the substance dried for 2 hours at 105° C.          .sup.7 referred to the substance baked 2 hours at 1000° C.        

    ______________________________________                                                           Extrusil                                                   ______________________________________                                        BET surface area.sup.1                                                                          m.sup.2 /g                                                                           35                                                   Average primary   nm     .sup. 25.sup.9                                       particle size                                                                 Tamped density.sup.2                                                                            g/l    300                                                  pH value.sup.3           10                                                   Sifting Residue   %        0.2                                                (acc. Mocker)                                                                 (45 μm).sup.4                                                              Drying loss       %       6                                                   (2 h, 105° C.).sup.5                                                   Ignition loss     %       7                                                   (2 h, 1000° C.).sup.5 6                                                SiO.sub.2.sup.7   %      91                                                   Al.sub.2 O.sub.3.sup.7                                                                          %        0.2                                                CaO.sup.7         %       6                                                   Na.sub.2 O.sup.7  %       2                                                   Fe.sub.2 O.sub.3.sup.7                                                                          %         0.03                                              SO.sub.3.sup.7    %      --                                                   Cl.sup.7          %        0.8                                                ______________________________________                                         .sup.1 DIN 66 131                                                             .sup.2 DIN 53 194 (unsifted), ISO 787/XI or JIS K 5101/18                     .sup.3 DIN 53 200 (in 5% aqueous dispersion), ISO 787/IX, ASTM D 1208 or      JIS K 5101/24                                                                 .sup.4 DIN 53 580, ISO 787/XVII or JIS K 5101/20                              .sup.5 DIN 55 921, ASTM D 1208 or JIS K 5101/23.                              .sup.6 referred to the substance dried for 2 hours at 105° C.           .sup.7 referred to the substance baked for 2 hours at 1000° C.        .sup.8 cannot be measured reproducibly                                        .sup.9 because of strong intergrowths, the size of the primary particles      cannot be accurately determined in silicates                                  .sup.10 total baking loss for 1 hour at 800° C.                        .sup.11 referred to the substance baked 1 hour at 800° C.         

The physical-chemical characteristics of the above products aredetermined using the following methods:

pH value, DIN 53 200

The pH value is determined electrometrically be means of a glasselectrode and a pH meter. As a rule, the pH of silicas is in the neutralrange and that of silicates in the weakly alkaline range.

Sifting residue, DIN 53 580

The sifting residue is a criterion of the fine particulate nature of thesubstance. In order to detect the non-dispersing portions, or thosedifficult to disperse and present in minute amounts in precipitatedsilicas and silicates, the sifting residue is tested according to themethod of Mocker. In this procedure, a suspension of silica is washed at4 bar water pressure through the sieve. The sieve is then dried and thesifting residue is weighed. The applicable sieves are the 45 microntypes, corresponding to 325 mesh in ASTM.

BET surface, DIN 66 131

The surface area of silicas and silicates is measured in m² /g by theBET method.

This procedure is based on the adsorption of gaseous nitrogen at thetemperature of liquid nitrogen. The areameter method by Haul & Duembgencan be applied advantageously. Calibration is required. Both the "inner"and the "outer" surfaces are determined.

Average size of primary particles

Electromicroscope photographs allow determining the mean size of theprimary particles. The diameters of about 3,000 to 5,000 particles aredetermined and their arithmetic average is then computed. As a rule, theindividual dual primary particles are not present as such but arecombined in aggregates and agglomerates. The "agglomerate" particle sizeof precipitated silicas and silicates depends on the particular grindingmethod.

Tamped density, DIN 53 194

This represents a measure of the weight of the powdery product. About200 ml silica are tamped 1,250 times into the measurement cylinder ofthe tamping volume meter. The tamped density is computed from the inputweight and the volume, and is stated in g/liter.

Drying loss, DIN 55 921

The precipitation products contain a small proportion of physicallybound water. After drying 2 hours in the drying cabinet at 105° C., mostof the physically bound water will have been removed.

Ignition loss, DIN 55 921

After 2 hour baking at 1000° C., the chemically bound water in the formof silanol groups also will have been removed. The ignition loss isdetermined from the substance dried for 2 hours at 105° C.

The FK 320 DS precipitated silica was steam-jet ground following dryingin the rotating cylinder.

The Durosil precipitated silica is unground and dried in a rotarycylinder.

The Sipernat 22 precipitated silica is spray dried.

The Sipernat 22 S is spray dried and ground precipitated silica.

The Sipernat 22 LS precipitated silica is spray dried and air jetground.

The Exclusil precipitated silica contains a slight amount of calciumsilicate.

The carbon blacks suitable for use with the granular bitumen of theinvention can be made conventionally, for instance, the methods forlampblack, gas black or continuous furnace black (ULLMANNS Enzyklopaedieder technischen Chemie, 4th Edition, Vol. 14, pp. 633-48).

In a preferred aspect of the invention, the carbon black known asPRINTEX XE2 with the characteristics below may be used.

    ______________________________________                                        Specific surface area                                                         per BET          (m.sup.2 /g)                                                                              1000                                             DIN 66 132/ASTM D 3037                                                        per iodine adsorption                                                                          (mg/g)      1000                                             DIN 53 582/ASTM D 1510                                                        (input 0.05 g)                                                                DBP-Adsorption   (ml/100 g)   370                                             DIN 53 601/ASTM D 2414                                                        (input 10 g)                                                                  pH value                       8                                              DIN 53 200/ASTM 1512                                                          Tamped density   (g/l)        140                                             DIN 53 194/ISO 787 XI                                                         Drying loss      (%)         max. 1                                           DIN 53 198/ASTM D 1509                                                        Ignition residue (%)         max. 1                                           DIN 53 586/ASTM D 1506                                                        Sifting residue per Mocker                                                                     (%)           max. 0.05                                      DIN 53 580/ASTM D 1514                                                        ______________________________________                                    

In accordance with another embodiment of the invention, the process forpreparing the granular bitumen is carried out by atomizing hot, liquidbitumen in a spray mixer of any suitable type and simultaneouslyintroducing the powdery coating and separating agent by means of a flowof cold air into the spray mixer.

In this aspect of the invention, the liquid bitumen droplets cool in theflow of cold air. During this stage, the bitumen droplets are clad bythe powdery coating or cladding substance and separating agent andthereby are preserved from caking and adhering to the boundary surfaces.

In the cold state, the bitumen will be solid. It must be molten beforebeing introduced into the spray mixer.

The processing of liquid and hot bitumen directly obtained from therefinery, or the stationing of the spray mixer in the refinery, is anespecially economical mode of carrying out the invention.

Preferably, the following parameters are observed in practicing theprocess of the invention:

    ______________________________________                                        bitumen temperature                                                                              >180° C.                                            cooling air temperature                                                                           <10° C.                                            bitumen viscosity when                                                                           70 cp.                                                     spraying                                                                      ______________________________________                                    

The granular bitumen product prepared in accordance with the inventioncan be mixed with further powdery cladding and separation agents.

The granular bitumen product of the invention retains the type-specificproperties of the input bitumen and following melting acts as a binder.

The portions of powder-cladding and separation agents may serve asadditives in various applications.

The granular bitumen of the invention offers the following advantages:

It can be manufactured in the refinery. In the course of the transfer ofthe mineral oil processing sites from the industrial or consumingcountries to the countries of petroleum extraction, problems may arisein transporting the "distillation bottoms" bitumen in the form of atough, elastic-viscous material.

Pouring the bitumen into blocks for transport requires melting at thesite of processing before introduction in the process for utilization.

The marketing of a powder material is more easily handled. Small tomedium sales quantities can be packaged in ecologically harmless paperbags. Beyond that, drums and bins can be used.

In general, cold bulk material is easier to meter and control than hotliquid material.

The mixing equipment can be simplified for the preparation of roadconstructions asphalt, both as regards bitumen stock and mixingtechnology.

The preparation and processing of bituminous roofing materials isfacilitated.

The manufacture of construction protective materials (for instancebituminous lacquers and paints) based on solvents or emulsions isfacilitated.

The granular bitumen of the invention is a cold applied, powdery binderwhich becomes suitable for use by heating on the spot as, for instance,by melting. Thereby, it is possible to carry out repairs at theconstruction site, on streets, bridges, roofs, and the like.

The granular bitumen product of this invention allows for simplifyingthe production of special materials as, for instance, insulating panelsby using the granular bitumen in hot pressing.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be further understood with reference to the drawingwhich shows an apparatus for carrying out the invention.

DETAILED EMBODIMENTS OF THE INVENTION Example

A granular bitumen product is prepared by the spray granulation method.The equipment includes a spray granulator made byLuco-Spruehmisch-Technic GmbH, a melting station and a mixer. Aconventional, cold-type bitumen is heated to form a melt in the meltingvessel. Then, the liquid bitumen is atomized in the spray granulator.The granulation of the bitumen takes place in conventional manner in thespray tower. Silica (Sipernat 22 S) is used as the powdering andseparation agent. The cooled granular bitumen is post-treated bytumbling in a mixer.

The melting station is composed of a vessel heated by strip heaters.However different heating, for instance with a double wall and fuel oil,is quite suitable.

The temperature in the vessel is thermostatically controlled. With thepresent day outfitting of the equipment, a temperature of about 250° C.can be achieved. For some types of bitumen difficult to melt, a highertemperature range is needed (300-350° C.).

The material is pumped out of the vessel. To compensate for the pulsesproduced by the reciprocating pump, a pulse damper is installed on thepressure side of the pump. The pulse damper is a pipe mounted on thepump's pressure side. This pipe is sealed at the top side by a flange. Amanometer is mounted on said flange. In operation, the pump first movesthe bitumen into the pulse damper, creating an air cushion. This aircushion compensates substantially for the pump generated pulse and whenthe bitumen is atomized makes possible an almost constant spray cone.

All conduits from the vessel are simultaneously heated up to 250° C. Theconduit from the vessel either goes to the spray granulator or back tothe vessel.

At an approximate temperature of 200° C. (the exact temperature being afunction of the kind of bitumen), the bitumen enters the spraygranulator made by the Luco Co. This equipment combines two procedures;namely, the techniques of the fluidized bed and of atomization. Thebitumen is atomized in the upper part of the tower. Simultaneouslysilica (e.g. Sipernat 22 S) is added as the powdery coating andseparating agent to the spray tower. The cooling bitumen particles areclad or coated with the silica agent which prevents the bitumen fromsticking to itself. The partially still hot granular bitumen dropsfurther inside the tower and arrives at the fluidized bed serving tofurther cool the granular bitumen. Only when the bitumen has given upalso its internal heat does it leave the spray granulator apparatus.Thereupon, the free-flowing bitumen product can be bagged or, if calledfor, post-treated such as by mixing.

The drawing shows the spray granulator. The spray mixing vessel forms avertically oriented spraying zone for spraying in the bitumen andcoating agent and for mixing the two together. This zone has an upperregion where the components are introduced and a lower region which islocated above and leads to the fluidized bed located beneath the spraytower. This vessel is 3 m high and 2 m in diameter. The height of thespray tower is determined by the falling distance required to cool thegranulate.

The vessel diameter shall be at least 1 m more than the largestspray-cone diameter formed in the upper region of the spraying-mixingzone. The purpose is to prevent the sprayed material from being atomizedagainst the wall. The spray cone diameter is determined empirically andmust be ascertained by prior trials. As regards bitumen, the value ofthe spray cone diameter can be obtained by calculating only with muchdifficulty.

Nozzles for single and binary substances and rotating disks can be usedfor atomization. Binary nozzles provide a smaller average particle sizethan single substance nozzles; that is, the total surface of thegranulate obtained from binary nozzles is substantially larger than thatfrom single substance nozzles. Accordingly, much less silica separationagent is required by single substance nozzles and furthermoreoperational difficulties hardly arise. Single substance nozzles with aminimum bore of 1 mm are used.

Smaller nozzle diameters result in undesired clogging. The minimumdiameter is determined empirically. The spray cone is selected as largeas possible (120°) in order to achieve optimal exchange of heat andmaterial.

The bitumen leaves the nozzle at a pressure of 12 bars. This nozzle hasa bore of 1.5 mm. Under these conditions, the bitumen granulate capacityreached is 76 kg/h.

According to the desired flow, the silica separation agent is meteredthrough a vibration chute to the tower. The granular bitumen drops intoa vibration fluidized bed. Two blowers deliver the air of fluidization.In the experimental equipment, one blower flow is 20 m³ /min. The secondblower output is 10 m³ /min. The air in the tower is evacuated above thefluidized bed through a filter by means of a third fan. The flow fromthis fan is 60 m³ /min. The excess air proportion is sucked through anopening 400 mm in diameter at the top of the tower as secondary air.This secondary air migrates in concurrent flow with the main productflow through the spray granulator. This design allows pulsed cooling ofthe just sprayed bitumen. A counterflow method, whereby the air would beevacuated from the top of the tower, also is suitable. In that case, thedwell time of the granulate in the tower would be increased.

Experiment has shown that the ambient air sucked in does not fully coolthe hot granular bitumen. Accordingly, cooling equipment was installednext to the tower to cool the air down to as low as 10° C.

The cooled granular bitumen exists from the spray granulator through abagging means. Where called for, the bitumen can be subjected to posttreatment. The purpose of this post treatment is precise adjustment ofthe silica separation agent content and treatment of the granulatesurface for complete cladding with the silica separation agent. A drummixer is used for this mixing type post treatment. Any other mixer willalso be suitable provided it is gentle in its effect on this granulate.

Further variations and modifications of the invention will be apparentto those skilled in the art from the foregoing and are intended to beencompassed by the claims appended hereto.

German priority application P 38 26 497.8-45 is relied on andincorporated by reference.

We claim:
 1. A friable, granular bitumen product comprising finelydivided bitumen coated with from 0.5 to 6% by weight of a powderycoating and separation agent selected from the group consisting ofsynthetic silica and carbon black.
 2. The friable granular bitumenproduct according to claim 1 wherein the said agent is present in theamount of 1.5 to 3% by weight.
 3. The friable granular bitumen productaccording to claim 1 wherein the bitumen has a bulk density of between400 and 800 g/liters.
 4. The friable granular bitumen product accordingto claim 1 wherein the bitumen has a particle size of between 500 and700 microns.
 5. The friable granular bitumen product according to claim1 wherein the silica is a pyrogenic or precipitated silica.
 6. Afriable, granular bitumen product comprising finely divided bitumencoated with from 0.5 to 6% by weight of a powdery coating and separationagent selected from the group consisting of synthetic silica and carbonblack, said bitumen product made by the process comprising atomizinghot, liquid bitumen into a spraying and mixing zone and simultaneouslyintroducing into said zone a powdery coating and separating agentselected from the group consisting of synthetic silica and carbon blackby means of the flow of cold air.
 7. The friable, granular bitumenproduct according to claim 6, wherein the temperature of the liquidbitumen is greater than 180° C. and the temperature of the cooling airis less than 10° C.